Tensions remain high in the Middle East, where the Palestinian militant organization Hamas has vowed to target Israeli political leaders for assassination. The warning follows Israel's assassination of Hamas founder and spiritual leader, Sheikh Ahmed Yassin on Monday. Hamas political leader Khaled Meshaal says no Israeli will be safe - from Prime Minister Ariel Sharon on down to the average person on the street. In interviews from Damascus, Syria, Mr. Meshaal said it is a duty to target the leaders of the enemy just as the enemy targets the leaders of what he termed the resistance. He said the message to Ariel Sharon is that blood begets blood.

Israel has routinely carried out targeted assassinations of Palestinian militant leaders. Hamas leader Sheikh Ahmed Yassin was killed in an Israeli missile strike Monday. Mr. Meshaal escaped an assassination attempt by Israeli undercover agents in Jordan in 1997. Hamas' new leader in the Gaza Strip, Abdelaziz Rantisi, was slightly injured in an Israeli missile strike in June of last year.

Immediately following Sheikh Yassin's assassination, some Hamas leaders vowed revenge also on the United States, seen as Israel's staunchest ally and protector.

But, Mr. Rantisi has backed away from that threat.

"We have just one enemy, the Zionists," he said. "The Americans are not our enemy."

Israelis are bracing for revenge attacks. On Thursday morning, soldiers blocked a street in downtown Jerusalem.

The soldier told people to get back. A suspicious package had been found, and the bomb squad arrived at the scene.

Two controlled explosions were set off. Such events are not unusual here, but right now, everyone is on edge. This time, the suspicious package contained nothing lethal. But people know it's only a matter of time before the next real explosion hits.

As the region remains on edge, 60 Palestinian officials and intellectuals have called on Palestinians to refrain from revenge attacks. An advertisement published Thursday in the PLO's Al-Ayam newspaper called on Palestinians to halt violence, saying this will only bring more and harsher Israeli retaliation that will not help the Palestinian cause. They called instead for a return to non-violent protests to end the Israeli occupation of the West Bank and Gaza Strip.